Television



3 Sheets-Sheet l TELEVISION DETECTR FIG. 2

FIG. 3

BIAS

March 27, 1956 Filed May 11, 1950 March 27, 1956 P C, GOLDMARK EVAL TELEVISION 3 Sheets-Sheet 2 Filed May 11, 1950 March 27, 1956 P. c. GOLDMARK ETAI. 2,740,071

TELEVISION Filed May l1, 1950 3 Sheets-Sheet 3 u; N N N N "l 1 N il m W Wl 3 m SN I g S,

ATTORNEYS TnLEviSioN Peter C. Goldmark, New Canaan, Conn., and James Reeves, New York, N. Y., assignors to Columbia Broadcasting System, Inc., New York, N.l Y., a corporationof New York Application May ii, 195o, serial No. 161,334

1s ciaims. (ci. sis- 30) t vision picture is largely a function of the number of lines per frame. -When the number of lines per frame and* the number of fields per second have been fixed, thehori"l zontal resolution is largely a function of bandwidth; With present-day standards of 525 lines per frame, 60'- f`ieldsl double-interlaced' per second, and aV videobandwidth`- of 'approximately four megacycles, the ihorizntali resolution is somewhat less than the verticali resolution."

ln the sequential type of color television systemg'forf example,l that described in Goldmark Patent 2,480,57L issued-August 30, 1949, the field frequency is consider-i" ably higher thanthat employedin black-and-white tele-1# vision, and consequently a greater bandwidth is required to obtain the same horizontal and vertical resolution. Due' to the'. great demand for channels in the radio frequency spectrum, it hasl been necessary to limit'the bandwidth' required for color televisionfin order to increase' the-1 number of channels available for. use, and serious'efforts' have been made to limit the video bandwidthemployed' in color television to that employed for black-and-white, namely, about four megacycles.

Although the additionof color more than compensates. forv the decrease in geometrical detail resulting fromlim-i' ited bandwidth, it is of course highly desirable. to minimize :suelta-effects. Even'in black-and-white"television, any vimprovement-in sharpness aids in equalizing the hori-` zontal and vertical resolutions. p

Thepresent invention is directed to improving the sharp# ness. or crispness of reproduced television pictureswithout changingthenumber of .lines per frame or number of fields per. second, and without requiring a wider trai1s missionchannel. It is particularly intended for use in home broadcast receivers. However, the v-invention'can be employed in monitoring receivers. at the broadcast station, and even in the transmission circuits where adequate bandwidth Vis providedafter the crispening signals have been added.

In accordance with the broad aspects of the invention, a videosignal is passed through a differentiating circuit which 'differentiates at least the higher frequencyfcomponents of the signal. The dilierentiatedsignal is then suppli'clto the reproducing device, such as a cathode7ray tub'e, along with the normal video signal. Advantageo'iisly,-a'v high-pass filter is inserted lin the channelto 2,740,071 Patented Mar. 27, 1956 the differentiating circuit so 'as to'avoid overloading thef diiferentiator -withstrong low-frequency signals.

The effect of adding the 'differentiatedfsignal to the normal Vsignal is to sharpenthe outlines of objects and.- improvethe contrast whereverv there Vare sharp changes;` from one light level to another in the` picture. The cir-* cuit appears to hasten the transition from black-to-white,

orfrom white-to-black, so that improved contrast is obtainedt The effect is observed not onlyat the edges of large objectsbut also in the fine detail of the repro-gl duced image.v For example, the whites of a persons eyes` 1 are more clearly discerniblel when thecrispening circuit'v is employed.

Considerable.improvement in the sharpness'and crisp-5" ness of pictures has been obtainedV by the use'of a'simpleI differentiating circuit, with or without a small amount of delay.' Further improvement may be obtained by clippingthe differentiated signal ata suitable level, amplifying it 1 if required, and supplying it to the reproducing devicealong vwith the normal video.A A small time delay be tween the` differentiated signal and the normal signal is often'advantageous to still further improve picture quality.

The invention will be more fully understood by reference-.to the following description of specific embodiments thereof, taken in conjunction with the drawings in which:

Fig. 1 is a block diagramv of a color television receiver using the lcrispening circuit of the invention;

- Fig. 2 is a simple block diagram illustrating one em-f bodiment of the invention;

Fig. 3 isa circuitdiagram of the output circuit of al representative televisionreceiver',.incorporating one eml' bodiment of. they circuit of the invention;

Fig. 4 is a block'diagramv of another embodiment of the invention;

Fig. 5. is a. circuit diagramof the embodiment of Fig. 4;

Fig. 6 shows waveforms illustrating ther operation of the circuit of Fig. 3; and- Fig. 7 shows waveforms illustrating theoperation of the circuit of Fig. 5.

Referring now to Fig. l, a television receiver is shown in which an incoming broadcast signal is amplified, con verted to an intermediate frequency and further amplified in l0. The sound portion ofthe broadcast signal is extracted at a suitable point and fed to discriminator and audio amplifier 11 for reproduction by loudspeaker 20. Thevideo signalis fed to detector and video amplifier 12.

From 12, the video signal is supplied to cathode-ray tube'- 13 either with or without the interposition of an addi-l tional video amplifier 14. The` video signal from 12 is also fed into the crispening circuit 15, and the output'of this circuit is likewise supplied to cathode-ray tube 13.

The video signal with accompanying synchronizing sig` nals is also fed to a sync separating .and sav/tooth gener# ating circuit l6 for supplying horizontal and vertical deilection Wavestto the cathode-ray tube via connections I7.

The description so far has been that of ak black-andwhite television receiver, and vtheinvention may appro priately be employed in such al receiver. However, it has special usefulness in connection with a color televi-' sion receiver of the sequential type, and accordingly Fig. l1 illustrates a color lter disk 18 rotating in front of the the face of the cathode-ray tube, an appropriate motor control circuit may be providedl in 16 and' used to control the operation of motor 19.

Fig 2 shows a-.video input.: at 21 which is suppliedll directly to the4 outputcrcuitatzz.- Tliefiiiput` at 21 may`-K be derived from the. detector and: video amplifier 12 yrif' f Filter disk 18 isdriven by motor 19 In order to maintain proper syn#` ig. 1 and the output circuit at 22 may be the cathodety tube 13. A video amplier 23 may be employed if :sired to increase the amplitude of the signals. The 'ispening circuit is here shown as a diierentiating cirlit 24 supplied with the video signals from 21. The lerentiated signal output is supplied to the output cirlit 22 which may be the cathode-ray tube 13 of Fig. l. the video amplifier 23 is employed, the output of dierltiator 24 could be combined with the output of ampli- :r 23 and the resultant wave fed to the output circuit. Fig. 3 is a circuit diagram corresponding to the block agram depicted in Fig. 2. In this circuit the differenating circuit which effects sharpening or crispening of .e image is enclosed by the dotted rectangle 24. The imainder of the circuit is that of a typical black-andhite television receiver with the addition of resistor 25 the cathode circuit of the cathode-ray tube which lows insertion of the differentiated signal at the cathode. Output tube 26 is supplied with the video signal at put 27 to the grid. Anode 28 is connected through ries peaking coil 29, load resistor 32, and peaking coil to a suitable B+ power supply. Additional compenvtion is provided by capacitor 34 shunting resistor 31. he video signal is supplied through coupling capacitor 5 to the grid of the cathode-ray tube 13. Suitable grid as for the cathode-ray tube is supplied by voltage diding resistors 36 and 37 in conjunction with the B+ lpply and a suitable source of negative voltage.

The bias on the cathode 38 of the cathode-ray tube obtained from a suitable source of positive voltage 39 conjunction with a variable D. C. voltage supply de- )ted brightness control. The brightness control volt- ;e and the bias source 39 act through a voltage divider rrmed by resistors 41 and 42 to supply the cathode bias. apacitor 43 serves to by-pass video frequencies. These rcuits are conventional and further elaboration is therere unnecessary.

The video signal is also supplied from the output circuit i'tube 26 to the crispening circuit through lead 43. The gnal is applied to the grid 46 of tube section 47 rough an input circuit comprising coupling capacitor 44 1d grid resistor 45. Tube section 47 is here shown as triode, but other types may be employed if desired. he time constant of the coupling circuit composed of tpacitor 44 and resistor 45 is advantageously selected eliminate the low frequencies present in the video sigtl so as to avoid overloading triode section 47. Time instants of 2.2 and 4.7 microseconds have been emoyed with success, but the values are not critical and nsideraole variation is possible. Indeed, in some cases ,e time constant may be selected so that no substantial tering takes place. A small resistance 48 is inserted in e cathode lead to triode section 47 to prevent parasitic zcillations, and a rheostat 49 is inserted to control the tin of the stage. lf desired, this control may be omitted 1d the stage designed to yield the desired amplification. The anode circuit of triode 47 contains a differentiating rcuit comprising inductances 51 and 52. The differeniting action is based on the formula e=Ldi/dt. The age is designed so that the anode current waveform is nilar to the video signal applied to the grid, so that e output voltage waveform is substantially the differen- 1l of the applied video signal. Duero the fact that the deo signal to the differentiating circuit is taken from e junction of peaking inductance 33 and load resistice 32, a certain amount of dilfcrentiation is contributed l inductance 33. The dilferentiation is then completed 1 tube 47 and the inductive differentiating circuit in its lode circuit. The connection of lead 43 to the top of ductance 33 was selected so as to avoid adding capacince to the normal video channel'. ln many cases the gnal to the differentiating circuit may be extracted from e video channel in such a manner'l that no 4preliminary ferentiation takes place. In this vevent the entire difrentiating action may be produced by the anode circuit of tube 47. Resistance 53 is inserted to provide a certain amount of damping, and its value may be selected depending upon the circuit constants employed. If desired, of course, this resistor may be omitted. Suitable anode voltage is supplied from B+ through the decoupling resistor 54 and by-pass condenser 55.

The differentiated signal in the anode circuit of triode section 47 is supplied through coupling capacitor 56 and grid resistor 57 to the grid 58 of the ampliler triode section 59. The time constant 'of' the coupling circuit is advantageously such as to eliminate low frequencies to avoid overloading, and if desired may be made substantially the same as the input circuit to triode section 47. Anode voltage is applied from B+ through decoupling resistor 54 and load resistor 61. A small cathode resistor S0 is inserted to prevent parasitic oscillations. Resistors 48 and 50 may of course be omitted if unnecessary for stability.

The output of triode section 59 is fed through coupling capacitor 62 to the cathode 33 of the cathode-ray tube.

The operation of the circuit of Fig. 3 will be understood more fully by reference to the waveforms of Fig. 6.

Fig. 6a is a square wave representing an abrupt transition from black level 63 to white level 64 and back. Due to the limited bandwidth in the video circuits at the transmitter and receiver, this square Wave will be distorted into a wave similar to that shown in Fig. 6b. The time of rise from' black level 63 to white level 64, or vice versa, is in general 1/2fo, where fo is the highest frequency in the pass band. The waveform is that which would normally be applied to grid 46 of the cathode-ray tube. No attempt has been made to show the exact phase between the waves of Fig. 6a and b, inasmuch as considerable change may take place in the transmitter and receiver circuits.

The waveform of Fig. 6b may be applied directly to dilerentiating tube 47. However, as before mentioned, the connection of lead 43 between peaking inductance 33 and load resistance 32 has the effect of providing a certain amount of differentiation which is completed by the differentiating circuit in the output of tube 47. Also, the connection has the eiect of discriminating against the low-frequency signal components whiie passing the highfrequency components to tube 47.

With the differentiating action of the anode circuit of triode 47, an output wave will be developed which, when inverted in phase by the subsequent amplifying section 59, is similar to that shown in Figs. 6c. The differentiated wave in Fig. 6c is shown in time phase with the Wave of Fig. 6b. Inasmuch as the wave of Fig. 6b is applied to grid of the cathode-ray tube, whereas the wave of Fig. 6c is applied to the cathode, the net effect on the picture reproduction is as though they were subtracted, yielding the wave shown in Fig. 6d.

It is clearly apparent that the slope of the .rise 65 in Fig. 6d is much greater than the rise 66 of Fig. 6b. Likewise, the fall 67 is Fig. 6d is faster than the fall 68 in Fig. 6b. Consequently, when the diierentiated signal is supplied to the cathode-ray tube the transition from black-to-white and from white-to-black is much faster than that produced by the video signal alone. Hence the apparent contrast and sharpness of the picture is considerably increased.

It will be noted that there is a slight undershoot 69 and overshoot 71 in the wave of Fig. 6d, but this has not been found to be particularly objectionable unless it becomes excessive. Indeed, undershoots and overshoots of 10% of the signal amplitude are often helpful in clearly delineating detail. The undershoot and overshoot in Fig. 6d is somewhat greater than 10% but the added crispness of the image is found to more than olset any deleterious effects. The amount of undershoot and overshoot may be controlled by varying the amplitude of the differentiated signal by means of rheostat 49. With andere smaller-,amounted differentiated `signal .the undershoot. and overshoot is reduced, butthe time of rise and.f.al1.vis.` increased. Amplitudes approximately as shown, withthe differentiated signal about half `the amplitude 'of the square wave, have been employed with success and have given good results. However, they may be changed to suitthe judgment of the designer.

It will also be noted that there is some phase shift of slopes 65 and 67 with respect toslopes 66 and 68 of Fig. 6b. InasmuchI as the phase shift is constant for `the higher frequencies, this has-.not `been found to be objectionable.

lf desired, the dilerentiated signal of Fig. 6c may beadded in phase `with the signal of Fig. 6b to yield the resultant illustrated in Fig. 6e. by using another phase inverting stage between-the differentiating circuit and the cathode of the cathode-ray tube, or by providing suitable circuit means for insertingboth signals at the grid ofV the cathode-ray tube, or by other appropriate means. Suitable means for directly combiningthe differentiating signal and the video signal Will be described in connection with Fig. 5.

In some television receivers there is excessive delay of the high frequencies with respect to the low frequencies in the normal video channel. Fig. 6b may overshoot on the top of rise 66 and at the bottom of 68. In such case the subtraction of the differentiatedsignal yielding the wave of Fig. 6d may be preferable to the addition illustrated in Fig. 6e, in order to avoid further increasing the amount of overshoot. In-

deed, insome cases the subtracted differentiated signal may partially compensate for the excessive high freV quency delay in the normal channel.

The frequencies which are important in producing rapid transitions from white to black and viceversa are pre-v dominantly those in the upper portion of the pass band.

With `a differentiating circuit, for example, that` shown in Fig. 3, the voltage-output at the lower frequencies-- is small, and the effect of the diierentiation increases with frequency. Thus the differentiation is most effective where-- It is desirable, when using a triodef for the differentiating circuit, to select the inductances such that their reactances are considerably lower thanthe it is .most needed.

plate resistance of the tube over most or all of the normal bandwidth. Thus the stage operates essentially as a constant current stage.

The values of the circuit components shown inFig. 3 are those used in a specific embodiment whch has been operated with success. -They are intended Vmerely'as anaid. to the readypractice of the invention and may be" departed from widely dependingupon the applicationv andthe vjudgment of `the designer.

Referring nowito Fig..4, -a more elaborate embodiment"` is shown'whch-is advantageous `in many cases where the additional cost is permissible. As shown in block form, c

thewideo signal: is fedrthrough-an amplifier 75 'from the quency componentsthereof, and 'then to a diiferentiator frequency content.`

This can be accomplished As a result the wave of A circuit'diagram vfollowingthe arrangement'of Fig. 4

is shownin FigrS. Aninput video signal at terminal 79 is fed through an 'input circuit to the grid of amplifier tube Sli- Theanode circuit of tube 81 includes a load;v resistance 82 :and peaking'inductance 83and is suppliedV witha voltagefrorna suitable B+ sourceV throughy def-ff' couplingre'lsistor 84and rcapacitor .85." The output vided.` Sflal., at. the.- .anbd is. SliPPled hIUgh. .lead 186 land. a,

suitable coupling network to amplifier-tube` 87 and-thttrlev to output terminal .88.

The videosgnal in the cathode circuitoftubeilgis supplied from anv adjustable potentiometer89 tlll'ough.Y coupling capacitor 91 and grid resistor 92 t`o thecontrol grid of tube 93. The time constant of the coupling cir.-

cuit is advantageously selected to eliminate low-frequency.

components and thereby prevent overloading tube 93, as

described'in connection with Fig. 3. Ampliter93 is here shown as of the pentode type with its cathode grounded, the screen grid supplied with suitable voltage from through decoupling resistor 94 and capacitor 95,'and1the` suppressor grid grounded.

The anode circuit includes the diierentiating..circuitindicated by the dotted outliney 96.- The dilerentiating circuit is composed of inductance 97 Ashunted by resistance.:

98, and a series inductance 99. This circuitfunctions similarly to that shown in Fig. 3 and need not be described again.

The dierentiated signal is then fed throughcouplings. capacitor 101 and resistor 102 to two oppositely poled crystal rectifiers 103 and 104. Crystal rectifier 103 is.. supplied with a suitable negative bias through resistor'll'S.

which is adjusted to clip the differentiated signal. ata

selected point below lthe A. C. axis thereof as indicated by dotted line 116.. The resultant separated negative peaks such as represented at 117 are supplied to theconl trol grid of tube 11'8.

Rectiiier 104 is supplied with a suitable positive bias.,

through resistor 119 to clip the applied differentiated signal, at a selected point above the A. C. axis such asrep.v

The resultant separated'. positive peaks as, represented' at 122 are fed tothe con.-`

resented by dot'ted line 121.

trol grid of tube 123. Suitable bias for tubes`118and y123:,is suppliedby the common cathode bias circuit corn.`

posedv of resistor 124 and capacitor 12S. The negativeA and positive bias applied to thegridsvof tubes 118 and 123.- through resistors 115 and`119 vwill ordinarily bey small! Hence ,the tubes will" compared to the cathode bias. operate on similar-portions of` their characteristics.

A common output load circuit denoted 126 is employed'H for tubes 118 and 123, and also for tube 87 in the normal video'ch'a'nnel. '-Hence the output signal `ajgniearirig at terminal 88 includes the normal video signal and thenegative-andpositive peaks of the differentiated signal." Theoutputsignal may vbe passed directly to the control grid or cathode of a cathode-ray tube for reproduction.-

If desired, however, subsequent amplification may bev provided, in which case it is desirable. to employ considerablyl widerbandwidths-than/that employed in. the normalvideo,

cha'mlel. y Thev functioning.ofthecircuit of Fig. 5 will be understood-morefclearly by a consideration of thewaveforms of Fig.` 7.l Figs. 7a, b and. c are similar to Figs. 6a, b and c buit'represent only the first portion of the waves, for simplicity.. The differentiated signal is the signal supplied from the output of tube 93 to the crystal recti?" tiers. It is` hereassumed that the clipping level of rectier 104hasbeen set at line 106, so that only the upper portion of the pulse is allowed to pass. This upper portion of the pulse `is shown-in Fig. 7d. The subsequent amplification in tube 123 is such as to increase the amplitude of the clipped portion to that shown in Fig. 7e. Waves 7e and 7bare added in the output circuit of tubes 123` and 87, andthe resultant wave appearing at terminal' 88, is that shown in Fig. 71. lt will be noted that the rise time represented by'slope 107 is substantially greater thanl slope 66 of Fig. 7b.and is somewhat greater than Vthat shown in Fig. 6e. The overshoot` 108 is somewhat small. er than the overshoot in Fig. 6a but is accomplishedv by' a-slightuundershoot 109. The small amounts of over harmful and, if harmful at all, are more than offset by' the increaselin'sharpness and crispness due tothe shorter rise time.`

While Fig. 7 illustrates' the/elect of thelcrispe'nin'g cir-- uit only for transitions from black to white, it will be nderstood that a similar effect takes place for transitions rom white to black, in which case clipping rectifier 103 ames into play.

A small amount of phase shift between the normal ideo signal and the differentiated signal at the output ircuit may often be employed with advantage. Generally peaking the amount of phase shift is small compared to 1e half-period of the highest frequency in the normal ideo pass band, that is, small compared to 1/2 fo. By mploying such phase shift, and also by adjusting the mplitude of the differentiated and clipped signal, the mounts of overshoot and undershoot may be altered within limits.

Fig. 7g shows a differentiated and clipped pulse which i similar to that of Fig. 7e except that it has a slightly maller amplitude and has been delayed approximately of the rise time. The result of adding the waves of iigs 7g and 7b is shown in Fig. 7h. It will be noted that 1ere is a slightly greater overshoot 111 but a considerably maller undershoot 112. Also, the slope 113 is more early in phase with the center of the transition from lack-to-white shown in Fig. 7b.

It will be apparent that by selecting different clipping :vels for rectifiers 103 and 104, by selecting different mplitudes of the output differentiated pulse which is to e combined with the original video signal, and by adlsting the delay of the differentiated signal, various derees of rise time, overshoot and undershoot may be obained. Also the phase of the rise may be altered. The ombined Waves illustrated in Figs. 7f and 7h have been ound to give good results in practice, but the exact shape nay be altered Within the judgment of the designer.

The delay described in connection with Fig. 7g may be ibtained in any convenient manner. In designing the diferentiating circuit 96, a certain amount of delay may be ncorporated therein which will produce the desired effect. tlternatively, additional delay means could be inserted. )n the other hand, phase-shifting means may be inorporated in the video channel, or in both channels to ive the desired relative phase.

In the foregoing description two specific embodiments f the invention have been described and illustrative waveorms given. It will be understood that the precise opervtion of circuits of this character is somewhat difficult to ,scertain under all conditions of use. Therefore, although he theory presented is believed to be essentially correct, t is not insisted upon and may be subject to considerably nore elaboration. Regardless of theory, it has been asertained by test that the circuits described do improve he sharpness and crispness of television images and have `onsiderable value when video bandwidths are limited.

ndeed, it is quite possible that some improvement will be p {esistance-capacitance differentiating circuits may oftenv e suitable, particularly where low impedance sources are Lvailable.

Furthermore, it is not necessary that the crispening letworkffeed directly into the reproducing device, here `hown as a cathode-ray tube. It could be inserted earlier n the video channels if desired. In such case it is desirtblc to increase the bande/ith of the channel between he crispening network and the reproducing device so that he increased sharpness of the image will not be lost due o subsequent impairment of the frequency components )f the differentiated signal. In general the bandwidth of he circuits after the crispening signal has been added ,hould be of the order of twice the normal bandwidth. l`hus, if the normal bandwidth is four megacycles, the :ircuits subsequent to the crispening network should preferably have a bandwidth extending to approximately eight megacycles, and even more would be advantageous if clipping is employed.

In addition to the variations and modifications suggested in the foregoing description, others will no doubt occur to those skilled in the art within the scope of the invention.

We claim:

l. In a television receiver having a picture reproducing device, apparatus for improving the crispness of reproduced pictures which comprises circuit means for supplying a video signal having frequency components within a predetermined bandwidth to said reproducing device, a differentiating circuit supplied with said video signal and adapted to differentiate at least the higher frequency components thereof within said predetermined bandwidth to yield substantially only the differentiated signal components thereof, and circuit connections for supplying differentiated signal components from said differentiating circuit to said reproducing device.

2. In a television receiver having a picture reproducing device, apparatus for improving the crispness of reproduced pictures which ycomprises circuit means for Supplying a video signal having frequency components within a predetermined bandwidth to said reproducing device, a filter circuit supplied with said video signal and designed and adapted to substantially remove the lower frequency components thereof and pass the higher frequency components thereof within said predetermined bandwidth, a differentiating circuit connected to the output of said filter circuit and adapted to differentiate said higher frequency components of the video signal to yield substantially only the differentiated signal components thereof, and circuit connections for supplying differentiated signal components from said differentiating circuit to said reproducing device.

3. ln a television receiver having a picture reproducing device, apparatus for improving the crispness of reproduced pictures which comprises a video amplifier connected to supply a video signal to said reproducing device, said amplifier having a predetermined video bandwidth, a vacuum tube having an input control circuit and an anode output circuit, connections between said video amplifier and said input circuit to supply said video signal to said tube, an inductive differentiating circuit in said anode output circuit adapted to differentiate at least the higher frequency components of said video signal within said predetermined bandwidth to yield substantially only the differentiated signal components thereof, and circuit connections between said output circuit and said reproducing device to supply differentiated signal components thereto, whereby differentiated signal components are supplied to said reproducing device together with said video signal to improve the crispness of the reproduced image. v l

4. In a television receiver having a picture reproducing device, apparatus for improving the crispness of reproduced pictures which comprises a video amplifier connected to supply a video signal to said reproducing device, said amplifier having a predetermined video bandwidth, a high pass filter connected to said video amplifier 1 ode output circuit having a reactance at the highest frequency within said video bandwidth which is low in comparison with the impedance of said tube to yield a differentiated signal wave corresponding to said higher frequencyy components, and circuit connections between said output circuit and said reproducing device to supply said differentiated signal wave thereto, wherebyl said differentiated signal vwave is vsupplied to said reproducing device togetherwith said video signal to improve the crispnessof` the reproduced image.

5. In a television receiver lincluding a picture reproduc-A ing ldevice having beam intensity controlling means, ap-y paratus for improving the crispness of reproduced pic-l tures which comprises circuit means for-supplyng a video signal to the beam intensity controlling means of said reproducing device, a differentiating circuit supplied with said video signal and adapted to differentiate at least the higher frequency components thereof, a peak separating circuit supplied with the differentiated signal from said differentiating circuit and adapted to passonlythe peak` portions thereof, and circuit connections between said,-

peak separating circuit and the beam intensity controlling means of said reproducing device to supply the peak portions of the differentiated signal thereto.

6. In a television receiver having a picture reproducing device, apparatus for improving the crispness of re-v produced pictures which comprises circuit means forv supplying a video signal to said reproducing device, a filter. circuit supplied with said video signal and designed and.

adapted to substantially remove the lower frequency device to supply the peak portions of the differentiated.A

signal thereto for reproduction.

7. In a television receiver having a picture reproducing device, apparatus for improving the crispness of reproduced pictures which comprises a Video amplifier connected to supply a video signal to said reproducing de-l vice, said amplifier having a predetermined video band-v width, a vacuum tube having and input control circuit and an anode output circuit, connections between said video amplifier and said input circuit to supply said video.

signal to saidtube, an inductive differentiating circuitiii.'

said lanode output circuit adapted to differentiate at least. the higher frequency components of said video signal to yield a corresponding differentiated signal wave, a clipping circuit connected to said output circuit to receive the differentiated signal therefrom, said clipping circuit passing substantially only the peak portions of the differentiated signal, and circuit connections between said clipping circuit and said reproducing device to supply the peak portions of the differentiated signal thereto for reproduction, whereby said differentiated signal wave is supplied to said reproducing device together with said video signal to improve the crispness of the reproduced image.

8. In a television receiver having a picture reproducing device, apparatus for improving the crispness of reproduced pictures which comprises a video amplifier connected to supply a video signal to said reproducing device, said amplifier having a predetermined video bandwidth, a high pass filter connected to said video amplifier' to receive said video signal therefrom and adapted to substantially remove the lower frequency components within said bandwidth and pass the higher frequency components, a vacuum tube having an input control circuit and an anode output circuit, connections between said filter and said input circuit to supply said higher frequency components to said tube, an inductive differentiating circuit in said anode output circuit to yield a differentiated signal wave corresponding to said higher frequency components, a clipping circuit connected to said output circuit to receive the differentiated signal therefrom, said clipping circuit passing substantially only the peak portions of the differentiated signal, and circuit connections between said clipping circuit and said reproducing device w-Supply the mamar-tions Qf-thgdiffersntiated Staub thereto for wander-tien Awhereby Said. ldifferentiated Sie 1 nal wave is supplied to said reproducing device .togetherI with said video signal to improve. the crispness ofthe..`

reproduced image.

amplifier to receive said video. signal and adapted to dif.- ferentiate at least the higher frequency components thereof to yield a corresponding differentiatedsignal wave, a

r clipping circuit connected .to said differentiating circuit and adapted to clip said differentiated sig-nal wave in posi.-4

tive and negative directions topass only positiveand negative peak portions thereof, and circuit connections. be-

tween said clipping circuitfand said reproducing device to supply the pealcportions ofthe differentiatedk signal..

thereto for reproduction, whereby said differentiated sigg rial wave is supplied to said reproducing device together.-

with `said videosignal to improvethe crispness of thereproduced image.

l0. In a television .receiver having. a picture reproducing device, apparatus for improving the crispness of reproduced pictures which comprises a video signal channel for supplying a video signal having frequency components within a predetermined..bandwidth, to'l said vreproducingifdevice, a differentiating channel ysupplied with said video signal, said differentiating channel being designed and adapted to ydifferentiate atleast. the higher frequency con. patients` of. said video signal Within said predetermined vbandwidth to yield/substantially only they differentiated tsignal .components thereof, circuit connections for supply. ing differentiated .components frcrn said differentiating]` channel to said reproducing device, and 4phase-shifting i means in one .of saidchannels lfor shifting the relative.

phase. of ysaidvideo and differentiated signals. t

ll. v In a television receiver khaving a picture reproducing.v device, apparatusffor improving the crispness of reproduced pictureswliich comprises a video` signal source, a video signal channel connecting said source with said.

reproducing device to supply said video signai thereto,

ya .differentiating channel connected to said source to re ceivesaid video signal, a differentiatingicircuit in said-i differentiating' channel. designed and adapted to differentiate at least the, higher frequency components of said video signal .t o yield a corresponding. `differentiated signal,

a clipping circuit connected to the output of said differentiating circuit to receive the differentiated signal therefrom, said clipping circuit passing substantially only the peak portions of the differentiated signal, circuit connections between said clipping circuit and Said reproducing device to supply the clipped differentiated signal thereto for reproduction, and phase-shifting means in one of said channels for shifting the relative phase of said video and clipped differentiated signal as supplied to said reproducing device.

l2. 1n a television receiver having a picture reproducing device, apparatus for improving the crispness of reproduced pictures which comprises a video signal source, a video signal channel connecting said source with said reproducing device to supply said video signal thereto, a differentiating channel connected to said source to receive said video signal, a differentiating circuit in said differentiating channel designed and adapted to differentiate at least the higher frequency components of said video signal to yield a corresponding differentiated signal, a clipping circuit connected to said differentiating circuit and adapted to clip said differentiated signal wave in positive and negative directions to pass only positive and negative peak portions thereof, circuit connections between said clipping circuit and said reproducing device to supply the clipped differentiated signal thereto for eproduction, and phase-shifting means in said differeniating channel adapted to delay said clipped differentiated ignal a small amount with respect to said video signal as upplied to said reproducing device.

13. In a television video circuit having an inputrcir- :uit and an output circuit, the combination which com- )rises circuit connections for supplying a video signal raving frequency components within a. predetermined Jandwidth from said input circuit to said output cirzuit, a differentiating circuit supplied from said input :ircuit and adapted to differentiate at least the higher :'requency components of said video signal within said )redetermined bandwidth to yield substantially only he differentiated signal components thereof, and circuit :onnections for supplying differentiated signal components :'rom said differentiating circuit to said output circuit.

14. In a television video circuit having an input circuit 1nd an output circuit, apparatus for improving the crispiess of pictures reproduced from a video signal which :omprises a first circuit connected to supply a video sig- :al having frequency components within a predetermined Jandwidth from said input circuit to said output circuit, a differentiating circuit supplied from said input circuit in shunt with said circuit and adapted to differentiate at least the higher frequency components of said video signal Within said predetermined bandwidth to yield substantially only the differentiated signal components there of, and circuit connections for supplying differentiated signal components from said differentiating circuit to said output circuit.

15. In a television receiver having a picture reproduc- ,ng device, the method of improving the crispness of regroduced pictures which comprises supplying a video sig :al having frequency components within a predetermined bandwidth to said reproducing device for reproduction, iifferentiating at least the higher frequency components 3f said video signal within said predetermined bandwith to yield substantially only the differentiated signal components thereof,` and supplying said differentiated signal :omponents to said reproducing device for reproduction.

16. In a television receiver including a picture repro- :lucing device having beam intensity controlling means, the method of improving the crispness of reproduced pictures which comprises supplying a video signal to the beam intensity controlling means of said reproducing device for reproduction, differentiating at least the higher frequency components of said video signal to yield a differentiated signal, separating the peaks of said differentiated signal from the remainder thereof, and supplying said separated peaks to the beam intensity controlling means of said reproducing device for reproduction.

17. In a television video circuit having an input circuit and an output circuit, apparatus for improving the crispness of pictures reproduced from a video signal which comprises a first channel connected to supply a video signal having frequency components Within a predetermined bandwidth from sai-d input circuit to said output circuit, a second channel supplied from said input circuit in shunt with said first channel and including a differentiating circuit adapted to differentiate at least the higher frequency components of said video signal within said predetermined bandwith to yield substantially only the differentiated signal components thereof, and connections for supplying diierentiated signal components from said second channel to said output circuit.

18. in a television video circuit having an input circuit and an output circuit, apparatus for improving the crispness of pictures reproduced from a video signal which comprises a first channel connected to supply a video signal having frequency components within a predetermined bandwidth from said input circuit to said output circuit, a second channel supplied from said input circuit in shunt with said first channel and including a differentiating cir cuit adapted to differentiate at least the higher frequency components of said video signal Within said predetermined bandwidth to yield substantially only the differentiated signal components thereof, said second channel including a peak-separating circuit supplied from said differentiating circuit and adapted to pass only the peak portions of the differentiated signal components, and connections for supplying the output of said second channel to said output circuit.

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